This study is concerned with cyclic AMP-dependent protein kinase from the parotid gland and a description of substrates of protein kinase in membrane fractions from the parotid gland. Particular emphasis is placed on the presence of protein kinase substrates in plasma membranes and the membranes of secretory granules. Phosphorylation of the membranes in the presence of protein kinase is being tested and studied kinetically. Individual substrates will be characteized by SDS-polyacrylamide gel electrophoresis. The presence of protein kinase in various fractions of the parotid gland is also being investigated. The possible effects of protein kinase on secretoy granule function is to be studied. This work will concentrate on the permeability characteristics of secretory granules and the effect of protein kinase on permeability.